1. Field of the Invention
The present invention relates generally to capacitor discharge ignition systems and more particularly to control arrangements to provide speed control of engines. 2. Description of the Prior Art
Various capacitor discharge ignition systems of the prior art have been developed to provide engine speed control and selective engine cut-off controls. A first category of CDI systems of the prior art utilize ignition timing control for the control of engine speed as for example as disclosed in U.S. Pat. No. 4,228,780 and in copending application Ser. No. 488,212 filed by Ronald J. Wolf on Apr. 25, 1983 which is a continuation in part application of Ser. Nos. 331,293 and 382,679 now abandoned, and as further disclosed in prior art patents cited therein. A second category of prior art CDI systems provide engine cut-off controls either by means of a kill switch connected directly to the charging source or by shut-off coils that are selectively switched in and out of the circuit. For example, U.S. Pat. No. 3,941,110 to Sekigushi discloses in FIG. 3 a kill switch that is closed to short circuit the generating supply that charges the charging capacitor. U.S. Pat. Nos. 3,894,524 and 3,960,128 disclose arrangements where a separate shut-off coil is selectively switched in and out of the circuit to provide shut off signals in a triggering network of the switching device. A third category of prior art CDI systems include control arrangements for limiting the speed of an engine, for example, as disclosed in U.S. Pat. Nos. 3,941,110 and 3,703,889.
U.S. Pat. No. 3,941,110 to Sekigushi is directed to a CDI system that includes in the embodiment of FIG. 5 an arrangement for preventing excessive rotation of the engine. A switching element controlling means 55 for an SCR switching element includes a monostable multivibrator 551 that outputs a trigger current signal over a time interval t.sub.g. The CDI system is arranged to operate in a fire-charge sequence. As the engine speed becomes excessive, the trigger current signal t.sub.g is maintained as shown in FIG. 7 until the charge phase such that the charge capacitor is not charged since the charging circuit is short circuited by the SCR switching element.
U.S. Pat. No. 3,703,889 to Bodig et al discloses a speed limiting arrangement for a CDI system wherein an RPM dependent control voltage is generated and applied to the control SCR. When a predetermined engine speed is exceeded, the SCR is triggered when the charge winding supplies charging current to the ignition capacitor 11. Thus, the ignition capacitor is shunted. The engine speed dependent control voltage is generated by an additional magnet 40 on the flywheel that creates a weaker magnetic field than the magnet that induces the charging voltage in the charging winding. The magnet 42 is arranged to induce the charging voltage in the charging winding 15 and to induce a trigger voltage in the primary winding of the ignition transformer to trigger the control SCR to discharge the capacitor 11 at the primary winding.
While the above described arrangements of the prior art are generally suitable for their intended use, it would be desirable to provide an improved and simplified engine speed control arrangement for a CDI system.